There has been an increased interest in the use of liquefied natural gas (LNG) both because of potential fuel gas savings and because of environmental concerns with existing fuels. LNG is of particular interest for busses because of the range of travel required of busses.
More fuel can be stored when the fuel is in a liquefied state but effective storing of LNG presents particular problems. Current LNG storage systems actually in use on automotive vehicles employ fuel tanks that are very heavy, complex and expensive. State-of-the-art tank systems are of a Dewar type and comprise a stainless steel tank disposed inside of a further steel tank with vacuum between the two tanks. The tank system is maintained at a low pressure (about 150 psi) and also requires a pumping assembly to maintain the vacuum between the two steel tanks.
Other tanks for the storage of LNG have been proposed. U.S. Patent Publication No. 2002/0053573 to Bowen et al discloses a storage container or vessel for natural gas made from a composite material and including a non-load bearing liner in contact with the vessel. The composite material is comprised of high performance fibers (such as E-glass, S-glass aramid, carbon and KEVLAR® fibers, as well as others including silicon carbide fibers, boron filaments and ultra-high molecular weight polyethylene fibers). The liner is made from a substantially impermeable material or materials, such as metallic foil, a synthetic polymer film, a combination of a metallic foil on a thin polymeric film, a metal coated polymer substrate and laminate of a metallic liner sandwiched between polymeric layers.
U.S. Pat. No. 6,460,721 to Bowen et al also discloses a container for storing pressurized liquefied natural gas (PLNG). The container comprises a composite vessel made of fibers (e.g., carbon, glass or a hybrid of carbon and glass) embedded in a cryogenic epoxy matrix, and a liner made of a substantially impermeable material (e.g., seamless aluminum) which provides a barrier for the PLNG stored in the container. An outer polyurethane coating is also provided.
U.S. Pat. No. 6,401,963 to Seal et al discloses a composite overwrapped pressure vessel including a liner made of titanium and a composite overwrap bonded by an adhesive to the liner, and including a protective epoxy coating over the overwrap, e.g., a filament-wound graphite epoxy overwrap.
In a commonly assigned U.S. Pat. No. 6,193,917 to the present inventor (Delay), a composite tank is coated with a nickel coating and wrapped with graphite fibers wetted with an epoxy resin. The resin is cured and a layer of insulating foam is then applied and cured.